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Effects of acidification and increased extracellular potassium on dynamic muscle contractions in isolated rat muscles
Author(s) -
Overgaard Kristian,
Højfeldt Grith Westergaard,
Nielsen Ole Bækgaard
Publication year - 2010
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2010.195727
Subject(s) - extracellular , potassium , chemistry , muscle contraction , biophysics , anatomy , biology , biochemistry , organic chemistry
Since accumulation of both H + and extracellular K + have been implicated in the reduction in dynamic contractile function during intense exercise, we investigated the effects of acidification and high K + on muscle power and the force–velocity relation in non‐fatigued rat soleus muscles. Contractions were elicited by supramaximal electrical stimulation at 60 Hz. Force–velocity (FV) curves were obtained by fitting data on force and shortening velocity at different loads to the Hill equation. Acidification of the muscles by incubation with up to 24 m m lactic acid produced no significant changes in maximal power ( P max ) at 30°C. More pronounced acidification, obtained by increasing CO 2 levels in the equilibration gas from 5% to 53%, markedly decreased P max and maximal isometric force ( F max ), increased the curvature of the FV relation, but left maximal shortening velocity ( V max ) unchanged. Increase of extracellular K + from 4 to 10 m m caused a depression of 58% in P max and 52% in F max , but had no significant effect on V max or curvature of the FV curve. When muscles at 10 m m K + were acidified by 20 m m lactic acid, P max and F max recovered completely to the initial control level at 4 m m K + . CO 2 acidification also induced significant recovery of dynamic contractions, but not entirely to control levels. These results demonstrate that in non‐fatigued muscles severe acidification can be detrimental to dynamic contractile function, but in muscles depolarised by exposure to high extracellular [K + ], approaching the [K + ] level seen during intense fatiguing exercise, acidification can have positive protective effects on dynamic muscle function.